Silverfox From United Kingdom, joined Mar 2001, 1058 posts, RR: 0 Posted (11 years 3 months 1 week 1 day 20 hours ago) and read 1696 times:
When i flew a BA 747 i was in the rear facing seat. On the take off run, as the engines spooled up the intakes had a 'cloud' form inside them. it remained for about 10-15 secs (i will check on the video) before disappearing.
What caused this? is it a normal phenomenom, or just the weather conditions at the time?
I havent checked any other intakes as i am normally behind or adjacent to them.
Any ideas etc?
Silverfox From United Kingdom, joined Mar 2001, 1058 posts, RR: 0 Reply 2, posted (11 years 3 months 1 week 1 day 20 hours ago) and read 1681 times:
Not worried at all. just fascinated by it. I thought it might have something to do with weather conditions, just needed a confirm. very spectacular in my opinion.
Now we are going to get all the 'neds' looking backwards on takeoff!!
LZ-TLT From Germany, joined Apr 2001, 431 posts, RR: 0 Reply 4, posted (11 years 3 months 1 week 1 day 19 hours ago) and read 1664 times:
A common phenomenon when taking off in high humidity and/or low air temperatures.
As air is sucked into the jet intakes or passes the wing's leading edge, it has a high velocity relatively to the aircraft's parts(ie, engine intake, wing and so on). Since the high velocity produces high dynamic pressure(in means of elementary fluid mechanic), but the sum of the dynamic, static and hydrostatic pressure for a given fluid remains always constant(Bernoulli's equation) and the hydrostatic pressure of the atmosphere depends only on weight, the increase of dynamic pressure is compensated by a drop in static pressure. Lower static pressure means, the condensation threshold for dissolved water vapour sinks, so the water vapours in the air condensate and form this fascinating fog. The same happens over the wing's leading edge.
There are a lot of photos here at a.net where you can see the same thing. A breathtaking sight indeed.